The present invention is in the field of implantable medical devices, and more particularly, is directed to devices useful as prosthetic menisci.
The meniscus acts in the knee joint as a crucial stabilizer, a mechanism for force distribution, and a lubricant in the area of contact between the tibia and femur. Without the meniscus, stress concentration occurs in the knee in conjunction with abnormal joint mechanics, and premature development of arthritic changes from collagen stress occurs.
In the prior art, treatment of injured or diseased menisci has generally been both by surgical repair and by excision. With excision, regeneration of meniscal tissue may occur. Additionally, it is known that meniscal fibrochondrocytes have the ability to migrate into a defect filled with a fibrin clot and form tissue apparently similar to normal meniscal fibrocartilage. When an adequate matrix scaffold is present within a meniscal defect, such meniscal fibrocartilage may be formed. Meniscal tissue is also capable of self-repair when exposed to bleeding tissues, and additionally, it is also known in the prior art that meniscal cells in tissue culture are capable of cell division and matrix synthesis. Replacement of an injured meniscus in an otherwise healthy joint may prevent arthritic changes and may stabilize the joint. In diseased joints, replacement of the meniscus may reduce the progression of the disease process, and may provide pain relief. Allografting or meniscal transplantation, is one method of replacement which has been executed both in dogs and in humans. However, this approach has been only partially successful over the long term due to the host's immunologic response to the graft, to failures in the cryopreservation process, and to failures of the attachment sites.
In alternative prior art replacement approaches, menisci have been replaced with prostheses composed of artificial materials. Such prostheses have been constructed of purely artificial materials in order to minimize the possibility of an immunological response. In addition, the use of such materials is believed to be advantageous because it permits construction of a structure which can withstand the high and repeated loads which are encountered in the knee joint, and because it can alter the joint mechanics in beneficial ways that biological materials would not tolerate. For example, a Teflon net has been used to replace the resected meniscus of a dog upon which fibrous ingrowth or regeneration was observed, although accompanied by significant chondral abrasion. A prosthetic meniscus has also been constructed from resilient materials such as silicone rubber or Teflon with reinforcing materials of stainless steel or nylon strands (U.S. Pat. No. 4,502,161). In addition, a meniscal component has been made from resilient plastic materials as disclosed in U.S. Pat. No. 4,085,466. Reconstruction of meniscal lesions have been attempted with carbon-fiber-polyurethane-poly (L-lactide) with minimal success.
Generally, the replacement of meniscal tissue with structures consisting of artificial materials has been unsuccessful, principally because the opposing articular cartilage of human and animal joints is fragile. The articular cartilage in the knee will not withstand abrasive interfaces, nor compliance variances from normal, which eventually results from the implantation of prior art artificial menisci. Additionally, joint forces are multiples of body weight which, in the case of the knee and hip, are typically encountered over a million cycles per year. Thus far, prior art artificial menisci have not been soft, durable, or lubricative enough, nor have they been able to be positioned securely enough to withstand such routine forces.
Prostheses, in general, have been devised out of at least some of the constituents of the structures which they are replacing, or out of materials not considered to be immunogenic to the body. For example, Yannas et al., fashioned endodermal implants, synthetic epidermis (U.S. Pat. No. 4,060,081), and sciatic nerve guides out of collagen and glycosaminoglycans, which are biochemical constituents of many body organs. By adjusting the pore size and axes of the pores and fibers comprising these structures, regrowth could be stimulated, and was, indeed, observed. Further regrowth has been advanced by seeding of the nerve guide with Schwann cells prior to implantation. However, even with the foregoing technologies which have been applied to the reconstruction of anatomical structures other than knee joints, a structure suitable as a prosthetic meniscus and constructed from natural materials has not been developed in the prior art.
Accordingly, it is an object of this invention to provide a meniscal replacement or prosthesis.
Another object is to provide a meniscal replacement, or prosthesis, which does not interfere with normal joint motion, which would lead to either a reduced range of motion, or focal concentration of force at other sites within the joint and therefore progressive cartilage destruction.
Yet another object is to provide a meniscal replacement or prosthesis which is biomechanically able to withstand normal joint forces and is able to function at those loads to protect the cartilage and stabilize the joint.
Still another object is to provide a meniscal replacement or prosthesis which acts as a scaffold for meniscal fibrochondrocyte infiltration, and which is subsequently replaced.
A further object is to provide a meniscal replacement or prosthesis which is composed of biocompatable materials having an organization equivalent to that of the normal meniscus; thereby not evoking an immunologic reaction, nor aggravating other joint structures.
Still a further object is to provide a meniscal replacement or prosthesis which is adapted for implantation by standard operative techniques, preferably transarthroscopically.